This invention relates to automobile instruments and more particularly to the display of a variable quantity such as engine speed using an illuminated display field which changes in area according to the variable quantity and which requires no rotating pointer or the like.
Automotive vehicles are typically equipped with a panel mounted in the driver""s field of view and containing multiple instruments for displaying variable quantities such as engine speed, road speed, engine temperature and oil pressure. Tachometers and speedometers are usually the larger of the instruments and are often placed side-by-side in the center of the panel.
Most automotive instruments employ pointers or xe2x80x9cneedlesxe2x80x9d which are pivotally or rotatably mounted to travel across a display field having numbers or other indicia arranged in an arcuate or circular pattern.
Particularly in automobiles equipped with automatic transmissions, the need for an exact engine speed reading of the type presented by the traditional tachometer is reduced. Moreover, there is a benefit to be derived from combining two instruments, such as the speedometer and tachometer, into a single display head.
The present invention provides an instrument for displaying automotive operating variables using an illuminated display field which varies in size in proportion to the monitored variable. Such an instrument requires no needle or pointer and can be readily combined with a second display which does use a pointer or needle, thus saving instrument panel space. The display field may, for example, be a circle or portion thereof the illuminated size of which varies in proportion to a transmitted data signal which, in turn, varies in proportion to the measured quantity. Where the measured quantity is engine speed, the illuminated shape grows in radial size from a minimum size for low engine RPM""s to a maximum size for high RPM""s to give the operator a visual indication of instantaneous engine speed.
In an illustrative embodiment hereinafter described, the display comprises a plurality of concentric circular bands which are progressively illuminated from a small diameter inner band representing low engine speed to a significantly larger diameter outer band representing higher engine speed. Intermediate bands may be individually illuminated to cause the illuminated area to grow in a step-wise fashion, the sizes of the incremental increases in illuminated area being a function of the desired resolution.
In another illustrative embodiment, the bands are the same color when non-illuminated but differ from one another in color when illuminated so that, for example, the display may grow from a small green band at low engine speed to a significantly larger diameter red outer band representing maximum engine speed. Other colors such as green, yellow and orange may be selected for intermediate bands.
In a still further embodiment, display of engine speed is combined in a single display head with a more traditional speedometer display utilizing a rotating needle in combination with a circular strip bearing numerical indicia of vehicle speed. This composite display may further include one or more digital displays; in the illustrated embodiment the supplemental digital display is for engine speed.
The various features and advantages of the invention will be best understood from a reading from the following specification in which several embodiments of the invention are described.